Chemical sensors can be used to analyze a wide variety of environmental and bodily gases, aerosols, and fluids for properties of interest. For example, exhaled breath condensate (EBC) is widely known to be a diagnostically important bodily fluid that can be safely collected. In particular, the breath from deep within the lungs (alveolar gas) is in equilibrium with the blood, and therefore the concentrations of molecules present in the breath is highly correlated with those found in the blood at any given time. Analysis of molecules in exhaled breath condensate is a promising method that can provide information on the metabolic state of the human body, including certain signs of cancer, respiratory disease, and liver and kidney function. Several different analysis methods including gas chromatography (GC), chemiluminescence, selected ion flow tube (SIFT), and mass spectroscopy (MS) have been used to measure different exhaled biomarkers, including hydrogen peroxide, nitrogen oxide, aldehydes, and ammonia. However, these methods vary significantly in sensitivity.
Another example of sensing application using body fluid is detecting breast cancer with saliva. The mortality rate in breast cancer patients can be reduced by increasing the frequency of screening. The overwhelming majority of patients are screened for breast cancer by mammography. This procedure involves a high cost to the patient. Moreover, the use of invasive radiation limits the frequency of screening. Recent evidence suggests that salivary testing for markers of breast cancer may be used in conjunction with mammography. Saliva based diagnostics for the protein c-erbB-2, a prognostic breast marker assayed in tissue biopsies of women diagnosed with malignant tumors, has shown tremendous potential. Soluble fragments of the c-erbB-2 oncogene and the cancer antigen 15-3 were found to be significantly higher in the saliva of women who had breast cancer than in those patients with benign tumors. Another recent study concluded that epidermal growth factor (EGF) is a promising marker in saliva for breast cancer detection.
Pilot studies indicate that the saliva test is both sensitive and reliable, and is potentially useful in initial detection and follow-up screening for breast cancer. However, currently saliva samples are typically obtained from a patient in a dentist's office then sent to a testing lab; it typically takes a few days to get the test results.
To fully realize the potentials of sensors for environmental, health related, chemical and biomedical applications, technologies are needed that will enable easy, sensitive, and specific detection of chemical or biomolecules at home or elsewhere. It is also desirable that a testing device allows concomitant wireless data transmission into preprogrammed destinations, such as transmitting breast cancer testing results to a doctor or clinic. If inexpensive technologies that can detect and wirelessly transmit testing results for environmental, health related, chemical and biomedical applications can be developed, early diagnosis of cancers or disease can significantly lower mortality and the cost of health care. In addition, real-time wireless remote sensing for chemicals in the environment may reduce the incidence of disasters by alerting to a chemical hazard.